In transceivers, an automatic gain control (AGC) block is used to attenuate or amplify an incoming analog signal such that the analog signal at its output is within the dynamic range of the sampling circuits that detect and convert the analog data into a digital bit stream. The AGC block typically includes a variable gain amplifier and a control loop that automatically adjusts the amplifier's gain.
In wireline transceivers, high loss channels will result in small signals at the receiver front end, while low loss channels will result in large signals that saturate the receiver front end. The AGC circuit, whose gain is determined through an automatic adaptation loop, attenuates large input signals and amplifies small input signals such that the signal at its output is never smaller than the sensitivity of the sampler circuit and never saturates the sampling circuit, both of which cause erroneous detection and bit errors. Accordingly, it is desirable to provide an AGC circuit with a wide gain range, high bandwidth, and good linearity with no parasitic in-band peaking across AGC gain settings.